The invention relates to a dental care or oral hygiene device with a handle, a head and a care part insertable in locking manner in a depression of the head and which by means of a resilient pressure piece on the back of the head acting by pressure action on the back of the care part can be ejected.
Dental care devices of the aforementioned type are particularly used as toothbrushes, so that hereinafter reference will only be made to the latter. However, they also cover devices which are exclusively used for massaging the gums or for caring for the interdental gaps.
Toothbrushes are required much more frequently than other types of brushes. The reason is the frequent use necessary for correct oral hygiene (up to three times daily) and the rapid wear resulting from this. In addition, Even in the case of relatively limited wear which would be acceptable with other brushes, a toothbrush has to be replaced, so as to always ensure an optimum effectiveness.
Due to the high toothbrush consumption, approximately 150 million per annum in Germany, there is an increasing problem of disposal and protecting resources, because the material fraction rendered unusable due to wear is extremely small compared with the total material and the total material to be disposed of, even in the case of a 100% recycling, cannot be processed to the same product, because the recycled material no longer fulfills the high quality requirements, which are vital e.g. for the bristle material of a toothbrush. Even if the known brushes with a replaceable brush part would fundamentally make it possible to only replace the brush part after wear, this problem has not hitherto been in the foreground and also in the case of standard brushes, such as cleaning brushes, body brushes, cosmetic brushes, etc. it is relatively unimportant, because the use period is much longer and the material ratio of unusable and still usable material is not in the same disproportion as with toothbrushes.
Finally, in connection with toothbrushes account must be taken of the special feature that they must be correctly usable by humans of all age classes and all education levels, so that the replacement of the brush part must be possible in a very simple manner and with limited force expenditure, whilst at the same time adequately securely joining the parts.
At present there are essentially two systems on the market. In the case of so-called replacement head brushes (EP 0 199 849 B1, DE 94 20 405 U1) the entire head with the bristles is detachably fixed to the handle. The locking fixing means are located on the handle substantially transversely to its longitudinal axis and on a shoulder of the head and are brought into engagement by the assembly of the head and handle in the longitudinal axial direction. Conversely the two parts can be detached by pulling apart in the longitudinal axial direction. These replacement head brushes are satisfactory from the use and hygienic standpoints. However, the plastics fraction of the head, which becomes waste when the bristles become worn, is still considerable. The further disadvantage arises that the fixing means are located in the transition area between head and handle, i.e. in an area where the greatest bending forces act during use. However, it is precisely in this area that the toothbrush is weakened by the constructional measures for the fixing means. This is particularly serious because, for use reasons, between the handle and the head it is desirable to have a slender and optionally resilient neck, which cannot be implemented with such replacement head brushes. Therefore replacement head brushes have already been proposed, in which the head is locked with the slender neck on the thicker handle. Thus, although the use advantage is substantially maintained, this is achieved at the cost of a larger amount of plastics waste. In addition, the risk also arises with all replacement head brushes, that in the case of incorrect locking or a failure of the locking system during use, serious injury can occur in the oral cavity.
With other known systems, to which belongs the toothbrush according to the preamble of claim 1, the bristles are fixed to a support in the form of a thin plate and said brush part is replaceably locked in the frame or casing-like head (DE 30 38 895, 37 24 640). The support is provided on its circumferential surface with ledge-like catches and the casing has corresponding channel-like depressions. On its back the support also has a pin, which engages in a hole in the bottom of the casing and forms on the back of the head an exposed pressure surface. The support is locked in the head and can be ejected by pressure on the pin. The plastics fraction to be replaced in the case of bristle wear is reduced to a minimum and the replaceable brush parts can be inexpensively manufactured due to the small amount of material used. However, hygienic and constructional problems arise as compared with replacement head brushes. In the gap necessarily present between the support and the casing cheek, which only dries inadequately, there is a deposition of dirt and accumulation of bacteria. This applies to a greater or lesser extent for the entire gap between head and support.
Thus, on its bristle side, the support is provided with an elastic, circumferential border (DE 37 24 640 C2), whose back sealingly engages against the front face of the casing cheek. This presupposes corresponding tensile forces drawing the support into the casing and consequently correspondingly high locking forces. In turn these make more difficult the insertion and ejection of the brush part. As locking takes place by self-closure, the locking means must be of a correspondingly large-volume nature, which requires considerable wall thicknesses on the head. Even more complicated is a construction (DE 296 00 398 U1), in which on all the sealing faces between the support and casing are provided elastic flat seals, which by a correspondingly high pretension simultaneously retain the brush part. The pretension must be completely absorbed by the casing cheek, which necessarily widens after a short time and a reliable hold of the brush part is no longer ensured.
Other proposals (DE 91 09 625 U1, DE 44 34 617 A1), which provide locking ledges in portionwise manner on the support circumference, lead to a corresponding reduction of the sealing of the gap, because the locking ledges and recesses are located in the sealing surfaces and very narrow tolerances must be respected, in order on the one hand to ensure a snug engagement of the sealing surfaces and on the other a reliable locking. It is scarcely possible to achieve such tolerances with injection moulded parts and the inexpensive plastics required for the head and handle. In addition, the casing cheek is constantly under elastic pretension due to the locking forces. Since plastics are not creep-resistant under tension (cold flow), there is a very rapid decrease to the tensional force of the casing cheek, so that the gap between cheek and support enlarges and the infiltration of dirt and bacteria is aided. As plastic fatigue and the resulting increase in the tolerances can scarcely be noticed by the user, he may only notice the failure of the locking means when cleaning the teeth. If the brush part is detached during use, it can once again lead to injury to the oral cavity and gingiva.
A very stable and durable connection of the brush part and head is brought in a known toothbrush (DE 41 04 314 A1) in that on the back of the support are shaped two mutually V-shaped ledges, which pass over the entire support length. They engage in a slot on the head opening outwards in V-shaped manner and which also passes over the entire length in its longitudinal axis. During insertion the ledges must be deformed inwards and towards one another to such an extent that they can pass through the narrowest cross-section of the V-shaped slot and then expand in said slot. Thus, the elastically deformed parts of the locking connection are located on the replacement part, where material fatigue is less important. The deformation forces on the ledges required for producing and detaching the locking connection are so high that the brush part can only be pressed or levered out with the aid of specially adapted tools. The need for such special tools not only leads to correspondingly high system costs for the consumer, but is prejudicial to a practical acceptance of the system by the market. This also applies because it is not possible to fulfil a requirement for avoiding injury, namely a smooth shape of the brush back. In addition, this toothbrush is also completely unacceptable for hygienic reasons, because the slot and ledges form several cracks, in which can be deposited dirt, toothpaste residues and bacteria. The same applies for another known construction (U.S. Pat. No. 4,543,679) with an expanding pin on the support, which engages in a V-shaped through hole on the back of the head.
In all the constructions with an exposed pin on the back as the pressure piece, the already described problem of the penetration of dirt and accumulation of bacteria arises. In addition, the back of the head is not smooth and gaps and depressions can become larger with increasing use times. The irregularities on the surface of the back can lead to mouth injuries.
The aforementioned disadvantages are largely removed in the already mentioned embodiment (DE 37 24 640 C2), in that the casing on the back is closed and the casing bottom wall thickness along a closed line is weakened in much the same way as a so-called film hinge, so that the bottom area within the weakening line is connected by means of a resilient connection to the remaining bottom area. The resulting pressure piece can be displaced when pressure is applied with the finger and can act directly on the support in order to eject the care part. This construction has the further advantage that the manufacturing tolerances for the locking means can be chosen narrowly without taking account of the pressure piece ejection function. However, it is disadvantageous that this construction necessarily only allows a small stroke or travel on the pressure piece. In addition, the head must be made from a relatively high-grade plastic, in order to ensure the spring characteristics for the pressure piece. In addition, fatigue fractures can easily occur in the area of the spring-like connection of pressure piece and bottom. As the spring articulation necessarily also requires gaps on the back of the head reducing the wall thickness, the hygienic requirements are also only inadequately fulfilled and here again injuries can occur in the oral cavity.
The problem of the invention is to so construct a dental care device of the last-mentioned construction, that the special hygienic requirements are fulfilled and the use characteristics improved.